A major outcome of the simplified theoretical model [1]} mentioned above
was to provide evidence of two transitions between extinction and survival of the population, depending on the turbulent intensity (for deep enough fluid layers). Our aim, here, was to explore the impact of a more realistic representation of the advecting velocity field on the survival-to-extinction transition, for which no analytical prediction is available, occurring at large turbulent intensity when biological production cannot compensate turbulent mixing to sustain the bloom in the well-lit region close to the surface. Using realistic parameter values for the biological dynamics [1]}, we then considered a domain with a fixed depth representative of the mixed layer, in the presence of flows of progressively increasing complexity, relying on a kinematic-flow approach [3]}. We first examined a velocity field possessing a single large-scale stationary mode, in the form of two recirculating cells spanning the horizontal extent of the system [4]}, [5]}. Such a spatial structure was intended to mimic the large-scale features observed in realistic flows, as those arising from buoyancy driven convection [5]}, [7]} or wind-driven Langmuir circulation [4]}, [9]}, [10]}. We then added time dependency in the form of lateral oscillations of such a flow pattern, and finally included spatially and temporally varying smaller scales.
